The invention relates generally to motion or force transmitting members such as push-pull and/or torsion rods, and deals more particularly with such a member made of a body of composite material and metal end fittings and having an improved form of connection between the body and each end fitting, the member being strong yet relatively light-weight.
Light-weight force and motion transmitting members of the type with which this invention is concerned are often used in aircraft as the weight of aircraft components is of great importance. For example, such members in the form of push-pull rods can be used to secure and adjust the pitches of helicopter blades as in Pertusio U.S. Pat. No. 3,129,766. This type of push-pull rod typically terminates at each end with a bearing which mates via a pin to an adjacent part so that the rod and adjacent part can pivot relative to one another as motions are transmitted from one to the other.
In addition to being light-weight, composite material rods in the broad class of the invention typically have a synthetic shaft and can be outfitted with corrosion resistant end fittings to make the rod durable.
A light-weight, composite material propeller shaft is disclosed in U.S. Pat. Nos. 3,553,978 and 3,592,884 to Williams and consists of a light-weight and relatively low strength core, end fittings attached to either end of the core, and a stiff tubular composite strength member completely surrounding the core and partially overlapping and adhering to the end fittings to form a rigid connection between the end fittings and the strength member. The strength member consists of a fibrous braid impregnated with a resin which serves to rigidify itself and the braid and to fix the resulting strength member to the end fittings. The core is made of a light material such as foamed polyurethane and serves primarily as an armature for receiving the braid and resin and holding the end fitting in place while the braid and resin are applied and cured. The portion of each end fitting which receives the composite strength member is cylindrical in shape and is either roughened by knurling or longitudinal grooves so that the strength member readily adheres to the end fittings.
U.S. Pat. Nos. 3,263,519 and 3,434,501 to Conrad describe the construction of flexible, motion transmitting cables each having a flexible conduit, wires within the conduit, and fittings at both ends of the conduit. The end fittings overlap the conduits and the conduits have irregularities such as grooves or flanges, and the end fittings are molded so that they interlock with the irregularities of the conduit.
Although light-weight push-pull or torsion rods have been proposed, further advances are deemed necessary to make such rods even stronger.
Accordingly, a general object of the invention is to provide such a rod which is stiff, light-weight, and strong, and has a fitting at either end or both ends to interconnect with other parts and transmit torsion, tension or compression forces between said other parts.
It is a more specific object of the invention to provide, in a stiff push-pull or torsion rod having an end fitting and a light-weight tubular shaft, means for anchoring the tubular shaft to the end fitting to yield a strong bond which resists torsion, compression, and tension forces so that the rod can transmit such forces from one end of the rod to the other without the end fitting breaking loose from or moving relative to the shaft.
Another object of the invention is to provide a specially shaped end fitting with conical and flared portions around which a stiff, tubular shaft fits snugly and interacts with the end fitting to yield a strong bond between the end fitting and tubular shaft withstanding tension and compression forces.